Low-frequency anomalous electro-optic behavior of colloidal systems (sign reversal and deviations from Kerr low) is considered in the light of electrically induced acoustic modes. The latter were recently detected and investigated in samples of isotropic spherical particles. Their linear dependence on field intensity explains the low-field "permanent dipole" behavior of charged colloids. The coupling of anisotropy and density fluctuations results in the complicated frequency curves of the electro-optic responses of anisometric particles.